Thanks for helping out Daniel.

The situation is actually quite complicated so I will try to give more details now as to what is happening.

At the heart of the problem is the partnership that exists between my ISP and Yahoo Mail.
Much to my dismay I learned years ago that all of my e-mail sits on Yahoo's servers, not my ISP's.

In the early days it was sufficient to set a username and password (of my choice) to log in using The Bat
and retrieve my e-mail. Many years ago this changed with the partnership between my ISP and Yahoo.

When they partnered, Yahoo decided that they would choose/set my password! I had no say in it whatsoever!
And they decided to make it very lengthy (16 letters put together randomly).
This password that they set could never be changed either.

I have 8 e-mail accounts with my ISP and many of them were never assigned this 16 digit password.

I don't know how The Bat logs into them to be honest when I use it. If I'm not mistaken it's impossible to see my passwords in
The Bat once they have been entered?

So as I said at the start, a couple of days ago I sent e-mail fr om one of these 8 accounts to another, using The Bat.
The e-mail was never received with The Bat. I logged into the account on the web at the Yahoo site and there was the e-mail sitting in
the account. I did this with two accounts. Same thing happened.

I was going to try to check a third account but couldn't because Yahoo threw up a message saying:
"Receive Verification Code
To begin, select your preferred channel to receive a 6-digit verification code.
Text:  ******5358 "

I don't know why it was asking to send a code, but I couldn't receive it because I don't use a cell phone anymore.
I spent over an hour yesterday on the phone with my ISP and they couldn't reset the password for me!
They said I needed to receive a verification code by cellphone!

So that's wh ere I currently stand.
Sometimes the e-mail is being received by The Bat, sometimes it isn't.

You mentioned above that the e-mail is being received but is copied to Inbox and marked as Read.
I checked and this is not the case.

Thanks Daniel I'll give that Google search a shot re: recovering passwords from The Bat.

One more thing.
A few years ago I discovered by trial and error files in The Bat that contained my passwords to accounts!
I believe the files were called ACCOUNT_LOG.TXT.

I was checking out these files yesterday to see if I could find my passwords (which are hidden in The Bat).
Something changed with these files and I don't know when it happened exactly.
The passwords are no longer mentioned in the file.

Before, the date, time, other details about the connection and the name of the password were listed in the file.
Could you check these files at your end (and others perhaps who are reading this thread)?
Can you see your passwords mentioned in these files?

If you somehow have access to these files from 5+ years ago, could you check also?
Do you know if this is a The Bat change, a Yahoo change or something else?

That information was very helpful at the time, because as I said, I can no longer see
the password inside The Bat once it was entered.

Go into the Account Properties for an account and look under Transport | Protocol Logging. That's where you enable POP.LOG.

(However, if you use an encrypted authentication method, I don't think the passwords will be logged.)

OK I just did extensive testing on all of my accounts (9)          
and only two are giving me problems logging in via the web (Yahoo).          
         
It's very confusing. This is how it works.          
         
At some point, as I mentioned above, Yahoo forced me to accept their          
own created passwords to be used with The Bat.          
         
It seems all of my accounts are able to use these Yahoo created passwords,          
although there have been delays in sending and receiving e-mails.          
         
The problems I'm having is when I want/need to log into Yahoo on the web          
to retrieve my e-mails.          
         
When I enter my e-mail address (does not end in .yahoo) , I am immediately re-directed          
to my ISP's website. Once I am there I am asked to log in to the account.          
Two e-mail accounts will not let me log in. I've tried using both the Yahoo provided password          
and the password I created with my ISP.          
         
One account immediately asks me to provide a cell phone number verify my log in (don't have a number).          
The other account just says the password does not work and asks is I want to reset it.          
I don't want to go any further when that comes up, for fear of being locked out of my account with The Bat.

But it's more than just that, and I don't know if The Bat is to blame, my ISP or Yahoo.
It comes down to this. I am now having the same problem that started this all off.
The reason I tried to log into my account using Yahoo on the web (instead of The Bat)
was because I wasn't receiving e-mails to certain accounts, when I sent them from different accounts.

I sent test e-mails from one account to two other accounts. It's been a couple of hours and they still
haven't arrived in the accounts! This shouldn't be happening.
I checked the passwords from these accounts and they work to log in, so the e-mails should be
received by The Bat.

Thanks for staying with me on this Daniel.
I'll start by answering your questions.Yes I am receiving other mail in the accounts.
Yes the accounts are active and are checked at regular intervals (also when pressing F2).
Yes I did check the Sent mail.
The log files do show activity, yes.
Yes the logs of the sending accounts confirm the messages were sent successfully.

Now let me get to some nitty gritty examples:

 

hello to j.t Mar 14   no     Web can't log in (wants to text to cell)  Log good send  

        to NW   Mar 14   no   Web yes    Log good send    Anand Mar 16 yes

        to t42 Mar 13     yes

        to t44 Mar 13     no     Web yes     Log good send

        to e.g Mar 12   no       Web yes     Log good send   Speakout Mar 15 yes

t-comp to hello Mar 15  no    Web can't log in    Log good send

         t42       Mar 15  no      Web can't log in     Log good send

         NW      Mar 14  no       Web yes     Log good send  

j.t to t42 Mar 13 yes

         tty            Mar 13  no      Web yes

         NW          Mar 13  yes    Web yes

I'll explain my short-hand notes.

hello to j.t. (these are two different accounts). Sending from hello to j.t. on Mar 14.
Result: no (meaning the mail was not received by j.t. account.)
I couldn't log into the account on the Web to check because they wanted to send me a text, to verify
my account.
The Send log showed the message was sent from hello account to j.t. account.

One more explanation.
hello to NW. Sending from hello to NW Mar 14
Result: no (meaning the mail was not received by NW account)
I logged into the account on the Web and yes, the mail was there.
The Send log showed the message was sent from hello account to NW account.
An e-mail was sent by a company called Anand Mar 16 and yes it was received by The Bat into NW account.

So you can see from the above notes that sometimes mail is received into the accounts in The Bat,
sometimes it is not received.
I suspect all of the mail is being received on the Web. There are a few accounts that I can't log into
as I mentioned because they are asking for cell phone verification.

One idea fr om me, since there are so many accounts: is the correct information (i.e., information that the server expects) given in TB's Account Properties for the From information?

Servers tend to quickly junk received messages wh ere the sender information does not match what is expected.